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Causes of ITP
The cause of ITP is unknown, but the disease involves two processes: the destruction of existing platelets and inadequate production of platelets to make up for those being destroyed.1-3
Platelets: Function and life cycle
Platelets are small, disc-shaped cell-like particles that are made in the bone marrowTissue inside the bones where blood cells are made. by cells called megakaryocytesCells in the bone marrow that make platelets. and circulate through the bloodstream. Platelets help stop bleeding by forming clots when blood vessels are damaged.4
Typically, a platelet is removed from the bloodstream after 9 or 10 days. But in an adult patient with ITP, antibodiesProteins made by the body's immune system to attack foreign cells. In ITP, antibodies attack the body's own platelets. attack platelets, so they are removed and destroyed much sooner—even as soon as a few hours after they enter the bloodstream. Antibodies may also attack the megakaryocytes, which may prevent these cells from making as many platelets as they typically would have.5
The importance of thrombopoietin
Thrombopoietin (TPO) is a protein produced in the liver that controls how many platelets are made by megakaryocytes. When platelet countsA measure of how many platelets are in the blood, usually expressed in thousands per microliter (e.g., 50,000) or in 109 per liter (e.g., 50 x 109/L). A count of 50 x 109/L is equal to a count of 50,000 per microliter. are normal, just enough TPO reaches the bone marrow to keep platelet counts level. If there are too few platelets in the bloodstream, more TPO is able to get to the bone marrow, so more platelets are produced.
In people with ITP, however, there usually isn't enough TPO reaching the bone marrow. This means that there are not enough platelets being produced to make up for the ones that have been destroyed.6
Nplate® is a man-made protein medicine used to treat low blood platelet counts in adults with chronic immune thrombocytopenia (ITP), when certain other medicines, or surgery to remove your spleen, have not worked well enough.
Nplate® is not for use in people with a precancerous condition called myelodysplastic syndrome (MDS) or low platelet count caused by any condition other than chronic (lasting a long time) immune thrombocytopenia (ITP). Nplate® is only used if your low platelet count and medical condition increase your risk of bleeding. Nplate® is used to try to keep your platelet count about 50,000 per microliter in order to lower the risk for bleeding. Nplate® is not used to make your platelet count normal.
Important Safety Information
What is the most important information I should know about Nplate®?
Nplate® can cause serious side effects:
Worsening of a precancerous blood condition to a blood cancer (leukemia): Nplate® is not for use in people with a precancerous condition called myelodysplastic syndromes (MDS) or for any condition other than chronic (lasting a long time) immune thrombocytopenia (ITP). If you have MDS and receive Nplate®, your MDS condition may worsen and become an acute leukemia. If MDS worsens to become acute leukemia you may die sooner from the acute leukemia.
Higher risk for blood clots:
- You may have a higher risk of getting a blood clot if your platelet count becomes high during treatment with Nplate®. You may have severe complications or die from some forms of blood clots, such as clots that spread to the lungs or that cause heart attacks or strokes. Your healthcare provider will check your blood platelet counts and change your dose or stop Nplate® if your platelet counts get high.
- If you have a chronic liver disease, you may get blood clots in the veins of your liver. This may affect your liver function.
Bone marrow changes (increased reticulin and possible bone marrow fibrosis): Nplate® may cause changes in your bone marrow, but these changes may improve if you stop taking Nplate®. These changes may lead to abnormal blood cells or your body making less blood cells. The mild form of these bone marrow changes is called "increased reticulin." It is not known if this may progress to a more severe form called "fibrosis." The mild form may cause no problems while the severe form may cause life-threatening blood problems. Signs of bone marrow changes may show up as abnormalities in your blood tests. Your healthcare provider will decide if abnormal blood tests mean that you should have bone marrow tests or if you should stop taking Nplate®.
Worsening low blood platelet count (thrombocytopenia) and risk of bleeding shortly after stopping Nplate®: When you stop receiving Nplate®, your low blood platelet count (thrombocytopenia) may become worse than before you started receiving Nplate®. These effects are most likely to happen shortly after stopping Nplate® and may last about 2 weeks. The lower platelet counts during this time period may increase your risk of bleeding, especially if you are taking a blood thinner or other medicine that affects platelets. Your healthcare provider will check your blood platelet counts for at least two weeks after you stop taking Nplate®. Call your healthcare provider right away to report any bruising or bleeding.
Lack or loss of response: If you do not experience results from Nplate®, your body may have created cells that are counteractive to Nplate®. Your healthcare provider will monitor your platelet counts and test your blood regularly to determine if this is an issue.
Blood test monitoring: Your healthcare provider will check your platelet count every week and change your dose of Nplate® as needed. This will continue until your healthcare provider decides that your dose of Nplate® can stay the same. After that, you will need to have blood tests every month. When you stop receiving Nplate®, you will need blood tests for at least 2 weeks to check if your platelet count drops too low.
What are the possible side effects of Nplate®?
- Nplate® may cause serious side effects. See "What is the most important information I should know about Nplate®?"
- The most common side effects of Nplate® are:
- Joint pain
- Trouble sleeping
- Muscle tenderness or weakness
- Pain in arms and legs
- Abdominal pain
- Shoulder pain
- Tingling or numbness in hands and feet
- These are not all the possible side effects of Nplate®. Tell your healthcare provider if you have any side effect that bothers you or that does not go away. For more information, ask your healthcare provider or pharmacist.
- If you have any questions about this information, be sure to discuss them with your doctor. You are encouraged to report negative side effects of prescription drugs to the FDA. Visit www.fda.gov/medwatch, or call 1-800-FDA-1088.
Please see Prescribing Information and Medication Guide for more information about Nplate®.
- Provan D, Stasi R, Newland AC, et al. International consensus report on the investigation and management of primary immune thrombocytopenia. Blood. 2010;115:168-186.
- Emmons RV, Reid DM, Cohen RL, et al. Human thrombopoietin levels are high when thrombocytopenia is due to megakaryocyte deficiency and low when due to increased platelet destruction. Blood. 1996;87:4068-4071.
- Nichol JL. Endogenous TPO (eTPO) levels in health and disease: possible clues for therapeutic intervention. Stem Cells. 1998;16(suppl 2):165-175.
- McNicol A, Israels SJ. Platelets and anti-platelet therapy. J Pharmacol Sci. 2003;93:381-396.
- Gernsheimer T. Pathophysiology and thrombokinetics in autoimmune thrombocytopenia. Blood Rev. 2002;16:7-8.
- Kaushansky K. The molecular mechanisms that control thrombopoiesis. J Clin Invest. 2005;115:3339-3347.